Here are some possibilities:
* Detrás: This is the most common opposite, meaning "behind."
* Atrás: This also means "behind" but can also be used to describe the opposite of forward movement.
* En la parte posterior: This means "in the back" and is more formal than the other options.
Example:
* Delante de la casa: In front of the house.
* Detrás de la casa: Behind the house.
It's important to consider the specific situation and the intended meaning when choosing the opposite of "delante."